Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$64.82	11.640%	$72.365	$72.37	$72.35	$72.40
Purchase #2	$47.56	12.366%	$53.4413	$53.44	$53.45	$53.40
Purchase #3	$38.29	5.474%	$40.386	$40.39	$40.40	$40.40
Purchase #4	$71.92	10.265%	$79.3026	$79.30	$79.30	$79.30
Purchase #5	$48.30	5.786%	$51.0946	$51.09	$51.10	$51.10
Purchase #6	$140.87	13.491%	$159.8748	$159.87	$159.85	$159.90
Purchase #7	$193.65	9.727%	$212.4863	$212.49	$212.50	$212.50
7 purchase totals =	$605.41		$668.9506	$668.95	$668.95	$669.00